Belief not only exists in man, as an essential part of his nature; but we may add as a separate proposition, that man knows what it is. There is belief in man, and a knowledge of that belief. It is no more possible for man to be without the knowledge of belief, than it is to be without belief itself. If a man believes, for instance, in his own existence, if he exercises any degree of faith in the physical and mental power he possesses, if in the affairs of life he relies more or less on the statements and promises of his fellow-men, if he believes in the fact of the revolution of the heavenly bodies, in the vicissitudes of the seasons, or in many other things which might be mentioned as things likely to control his belief, it is obvious that he knows, and that he cannot help knowing what natural belief or faith is, by his own inward experience. The knowledge of the thing, as well as the fact or existence of the thing, is involved necessarily in the constitution of the mind itself. And it is in that constitution, therefore, that we must seek for a knowledge of it. In other words, we obtain a knowledge of belief by a reference to our own inward consciousness; and we cannot obtain an adequate knowledge of it in any other way.
It should be added, however, that, while, by turning the mind inward upon itself, we know what it is, we are, nevertheless, not able to define it. It is admitted, that it is not possible to give a definition of belief or faith, which, independently of inward experience, will render it easy to be understood. But this difficulty, whether it be regarded as greater or less, and which on a close examination will be found to be more formidable in appearance than in reality, is not limited to belief. All other states of mind, which are truly simple and undefinable, are better known by a reference to our own consciousness, than by any statements in words.
— edited from The Life of Faith (1852) Part 1, Chapter 1.
